That's the advice I give to aspiring app store millionaires: on average there's no money in the app store, but there's plenty of money to be made making apps for someone else. Throw something on the store that's above the level of flashlight app, and point to it when in contact with a potential employer. There is no ??? step, you just move straight to Step 4: Profit.
People may think "If I write something and it gets enough attention, facebook or google might buy me out" or something to that effect. Basically a get rich quick kind of deal.
You only have to write one! thing, cash a multi million dollar check and be set.
While that may have happened in the past a couple of times, wanting to start an open source project just because of that possibility would be nearsighted. But starting such a project to promote oneself is not.
It is a great addition to your CV. Something future employers can directly check up on.
Then you can get the job. The App only appears to help.